Remove the six screws from the rear of the case as shown in the 1st picture, screw tye show in the second.

Finally, remove the two screws from the rear feet on the underside of the unit. Positions and score type is shown in the third photograph.

Now is a good time to plug in the power cable and raise the unit's lid, if you do not want to do this with the covers off.

Now just pull the rear cover off, it will expose a big aluminium, heatsink.